IN-VIVO NGF TREATMENT INCREASES PROLIFERATION IN THE PRIMARY SYMPATHETIC-GANGLIA OF CHICK-EMBRYOS

Nerve growth factor (NGF) is considered to be a target-derived surviva l or differentiation factor for neural crest cells of the sympathoadre nal lineage. However, exogenous NGF was found to have a positive effec t on the size of the primary sympathetic ganglia (PSG) of the chick em bryo, well before sympathetic innervation of the periphery. We have de termined the cellular mechanism of NGF's action on the PSG by quantify ing both proliferation and apoptosis. The proportion of PSG cells in S -phase is nearly double in NGF-treated embryos compared to that in con trols, strongly suggesting that NGF acts as a mitogenic factor. NGF re duced the low level of apoptosis at this stage as well. Since trkA has not been detected in the avian sympathetic ganglia until later in dev elopment, we suggest that these early effects of exogenous NGF may be mediated by the low-affinity neurotrophin receptor, p75, which is expr essed from neural crest migration stages. (C) 1997 Academic Press